Some helpful PHP training exercises

I love to challenge my knowledge on a regular basis, just to keep up with the technology and to keep my mind flexible and adaptive. As I am quite certain I am not the only one who likes to do this, I thought it might be nice to put up a page where I will cultivate a list of PHP training exercises for you, so you can use these PHP training exercises to train or keep up your PHP programming skills.

At the time of writing I have written out 4 exercises for you to do, which you can find here (or in the “My pages” section on this website).
I would really like to learn from your solutions, so please put them in a github gist and paste the link in the comments..